This invention concerns apparatus for companding non-standard television signal encoding information. In particular, this invention concerns such apparatus employed by a system for generating a widescreen television signal which is compatible with a standard television signal receiver.
A conventional television receiver, such as a receiver in accordance with NTSC broadcast standards adopted in the United States and elsewhere, has a 4:3 aspect ratio (the ratio of the width to the height of a displayed image). Recently, there has been interest in using higher aspect ratios for television receiver systems, such as 2:1, 16:9 or 5:3, since such higher aspect ratios more nearly approximate or equal the aspect ratio of the human eye than does the 4:3 aspect ratio of a conventional television receiver. Video information signals with a 5:3 aspect ratio have received particular attention since this ratio approximates that of motion picture film, and thus such signals can be transmitted and received without cropping the image information. However, widescreen television systems which simply transmit signals having an increased aspect ratio as compared to conventional systems are incompatible with conventional aspect ratio receivers. This makes widespread adoption of widescreen systems difficult.
It is therefore desirable to have a widescreen system which is compatible with conventional television receivers. One such system is disclosed in a copending U.S. patent application Ser. No. 078,150 of C. H. Strolle et al., titled "Compatible Widescreen Television System", filed July 27, 1987. It is even more desirable to have such a compatible widescreen system with provisions for enhancing or extending the definition of the displayed image so as to provide extra image detail. For example, such widescreen EDTV (extended definition television) system may include apparatus for providing a progressively scanned image.
In a compatible widescreen system, it may be necessary to transmit auxiliary video information together with existing standard information, e.g., in frequency interleaved form. It is desirable to convey such information via an auxiliary signal or signals with a large amplitude so as to enhance the signal-to-noise ratio of the auxiliary information. However, a large amplitude auxiliary signal can lead to unwanted interference with the standard video information intended to be processed by a standard receiver. Thus, one is faced with the dilemma of using a large amplitude auxiliary signal to maintain a good signal-to-noise ratio, or using a small amplitude auxiliary signal to prevent interference with standard video information. This dilemma is resolved in accordance with the principles of the present invention.